Convert the sprite task to the grunt convention

[LaurentGoderre]

Convert the task options from

  sprites: {
      icons36: {
          src: ['src/img/icons36/*.png'],
          css: 'src/css/icons36.css',
          map: 'src/img/icons36.png',
          output: "scss"
      }
  }

to

  sprites: {
      icons36: {
          options: {
              css: 'src/css/icons36.css',
              map: 'src/img/icons36.png',
              output: "scss"
          },
          src: ['src/img/icons36/*.png'],
      }
  }